Battery-less noncontact data carriers include a noncontact IC card which performs proximity communication by electromagnetically-induced binding using a frequency in an HF (High Frequency) band, and a noncontact tag which performs a longer-distance communication relative to the proximity communication, using an electromagnetic wave of a frequency in a UHF (Ultra High Frequency) band or a SHF (Super High Frequency) band. Many of these noncontact data carriers are operated with a power source that is obtained from a signal received by radio communication from a reader/writer.
However, there is a current situation where the noncontact tag is restricted in reception power which is obtained from the reader/writer as compared with the noncontact IC card performing proximity communication, and it is difficult to enhance the performance or increase the circuit scale which might cause an increase in power consumption.
In order to solve this problem, in recent years, a noncontact data carrier such as a noncontact tag which is equipped with a battery has been put to practical use (refer to Patent Document 1). The noncontact data carrier having the battery ensures a larger power relative to a battery-less data carrier by combining the power supply obtained from the reader/writer and the power supply obtained from the battery, and thereby performs complicated data processing and large-volume data processing for which stability of the power supply is required.
Hereinafter, a description will be given of a conventional battery-equipped noncontact data carrier. FIG. 18 is a diagram schematically illustrating the construction of a communication system comprising a conventional noncontact data carrier (referred to as a responder in FIG. 18) having a battery (referred to as a power supply part in FIG. 18), and a reader/writer (referred to as an interrogator in FIG. 18) which performs communication by a microwave with the noncontact data carrier. FIG. 19 is a waveform diagram illustrating the operation at startup of the conventional noncontact tag.
With reference to FIG. 18, the conventional battery-equipped responder 144 comprises an antenna 151 which receives a signal from the interrogator 141 and transmits a signal to the interrogator 141, a directional coupler 156 which transmits a transfer signal outputted from a transfer circuit 152 to the antenna 151 and transmits the signal received by the antenna 151 to a distributor 157, the distributor 157 which power-distributes the reception signal transmitted from the directional coupler 156 to a reception circuit 153 and to a wave detection circuit 158, a clock extraction circuit 156 which extracts a clock signal and a startup command from the output of the wave detection circuit 158, a judgment unit 160 which judges whether the extracted startup command matches a predetermined reference command for judgment or not, a CPU 161 which performs recognition of a command from the interrogator 141, processing based on the command, and generation of a response to the interrogator 141, a power supply unit 155 which supplies a power to the respective circuits in the responder 144, and a switch 154 which performs control for starting or stopping power supply from the power supply unit 155 on the basis of the judgment result of the judgment unit 160.
Power supply is continuously performed from the power supply unit 155 to the clock extraction circuit 159 and the judgment unit 160. Further, the directional coupler 156, the distributor 157, and the detection circuit 158 are operated with the power source received from the interrogator 141.
In this construction, when the responder 144 receives a signal including a startup command as shown in FIG. 19(a) from the interrogator 141, the received signal is transmitted through the directional coupler 156 and the divider 157 and detected by the wave detection circuit 158 in the responder 144. Then, a wave-detection signal (FIG. 19(b)) obtained in the wave detection circuit 158 is input to the clock extraction circuit 159, and the startup command is extracted. The startup command extracted by the clock extraction circuit 159 is input to the judgment unit 160, and it is judged whether or not a code of the startup command matches a code of a startup command for judgment which has previously been set. When there is a match, the output level is changed to turn on the switch 154 as shown in FIG. 19(c). When the switch 154 is turned on, power supply is started from the power supply unit 155 to the transmission circuit 152, the reception circuit 153, and the CPU 161, and consequently, the responder 144 is started up.
Patent Document 1: Japanese Published Patent Application No. 2005-80205